A stent is an elongated device used to support a luminal wall. A stent, along with a graft cover or liner, together provide an unobstructed conduit for fluid flow in the area of a stenosis. Such a stent-graft would typically have a tubular graft layer covering, or lining, the inside or outside of the stent (or both), thus providing a fluid conduit to bypass a stenosis or otherwise diseased body passageway.
Various types of stent architectures are known in the art, including many designs comprising a filament or number of filaments, such as a wire or wires, wound or braided into a particular configuration. Included among these wire stent configurations are braided stents, such as is described in U.S. Pat. No. 4,655,771 to Hans I. Wallsten and incorporated herein by reference. The Wallsten patent is only one example of the many variations of braided stents known in the art and thus is not intended to be a limitation of the invention described herein later. Braided stents tend to be very flexible, having the ability to be placed in tortuous anatomy and still maintain patency. The flexibility of braided stents make them particularly well-suited for use in intraluminal delivery where the lumen of the vessel becomes contorted and irregular both before and after placement of the stent.
The most common use of stents and stent-grafts is in the vascular system, in which stents and stent-grafts having a first small diameter compressed configuration may be introduced into a body lumen at a point remote from a site in that lumen in need of repair and then transported through that lumen, typically through a catheter, to that site. Once the site in need of repair is reached, the stent or stent-graft is either expanded or allowed to expand to a second, expanded configuration to provide an open passageway through that site.
Many of these braided stents have the problem, however, of either being too rigid such that intraluminal delivery and placement becomes difficult, or too flexible (at the cost of reducing radial strength) such that radial expansion forces exhibited at the site of treatment are insufficient to adequately maintain an open passageway through the site. Moreover, by increasing the radial strength of a stent, one typically reduces flexibility, because the stent is more rigid. Likewise, by increasing flexibility, radial strength is often sacrificed.
Thus, there is still a need to provide a fully-supported stent-graft that is flexible enough for navigation through tortuous lumina but rigid enough to properly anchor the device and maintain patency through the device at the site of treatment.